1. Field of the Invention
The invention relates to a technical field of making a determination on an abnormality in an electrically heated catalyst provided in an exhaust passage of a plug-in hybrid vehicle.
2. Description of the Related Art
In the background art of the invention, there is proposed an art for making a determination on an abnormality in an electrically heated catalyst (hereinafter referred to as an EHC as well) disposed in an exhaust passage. For example, Japanese Patent Application Publication No. 8-61048 (JP-A-8-61048) proposes an art for making a determination on an abnormality in an EHC on the basis of a catalyst temperature, a catalyst resistance, an electric power consumption, and the like at the time of energization of the EHC. Further, Japanese Patent Application Publication No. 11-210448 (JP-A-11-210448) describes a hybrid vehicle provided with an EHC.
In recent years, there have been developed plug-in hybrid vehicles using as motivity an electric power obtained through charging from an external electric power supply such as an electric power supply for home use or the like. In making a determination on an abnormality in an EHC provided in such a plug-in hybrid vehicle, the following problems are assumed.
In a plug-in hybrid vehicle, the electric power of a battery as an output tends to change in accordance with the running condition set by a driver. In some cases, therefore, a stable electric power for an EHC cannot be ensured to make a determination on an abnormality, the accuracy in making a determination on an abnormality is not guaranteed with ease, and an erroneous determination is made. In order to prevent such an erroneous determination and the like, it is conceivable to limit the output of the battery, which is used for running, with a view to thereby ensuring a stable electric power during a determination on an abnormality. However, when this measure is adopted, the energy for running that is accumulated in the battery is consumed to make a determination on an abnormality. Therefore, a deterioration in EV running performance or a deterioration in energy efficiency resulting from an increase in the load imposed on an engine may be caused. Further, since the plug-in hybrid vehicle is originally intended for the enlargement of EV running performance, the electric power of the battery tends to be used for EV running by priority. It is therefore considered that the electric power for making a determination on an abnormality in the EHC is not ensured and that the frequency with which a determination on an abnormality is made decreases.
On the other hand, while the vehicle is running, a changeover is made among EV running by a motor using an electric power from the battery, HV running accompanied by the start-up of an engine, and the like, depending on various conditions. It is therefore difficult to keep the temperature of the EHC constant. Further, out of consideration to the influence of a disturbance such as head-on wind, the processing itself of making a determination on an abnormality in the EHC tends to be complicated. In addition, when an attempt is made to give priority to the securement of the accuracy in making a determination on an abnormality in such a case, a determination on an abnormality is made only on a limited condition. As a result, the frequency with which a determination on an abnormality is made tends to decrease.
Neither Japanese Patent Application Publication No. 8-61048 (JP-A-8-61048) nor Japanese Patent Application Publication No. 11-210448 (JP-A-11-210448) describes how to make a determination on an abnormality in an EHC provided in a plug-in hybrid vehicle appropriately.